1. Field of the Invention
This field of art to which the claimed invention pertains is catalytic composites and processes useful for treating sour petroleum distillates. More specifically, the claimed invention relates to catalysts and catalytic processes especially useful for the treatment of sour petroleum distillates to effect the oxidation of mercaptans in the distillate to disulfides.
2. Description of the Prior Art
Processes for the treatment of sour petroleum distillates wherein the distillate is treated in contact with an oxidation catalyst in the presence of an oxidizing agent at alkaline reaction conditions have become well known and widely practiced in the petroleum refining industry. Said processes are typically designed to effect the oxidation of offensive mercaptans contained in a sour petroleum distillate with the formation of innocuous disulfides--a process commonly referred to as sweetening. The oxidizing agent is most often air. Gasoline, including natural, straight run and cracked gasolines, is the most frequently treated sour petroleum distillate. Other sour petroleum distillates include the normally gaseous petroleum fraction as well as naphtha, kerosene, jet fuel, fuel oil, lube oil, and the like.
A commonly used continuous process for treating sour petroleum distillates entails treating the distillate in contact with a metal phthalocyanine catalyst dispersed in an aqueous caustic solution to yield a doctor sweet product. The sour distillate and the catalyst-containing aqueous caustic solution provide a liquid-liquid system wherein mercaptans are converted to disulfides at the interface of the immiscible solutions in the presence of an oxidizing agent--usually air.
Sour petroleum distillates containing more difficultly oxidizable mercaptans are more effectively treated in contact with a metal chelate catalyst disposed on a high surface area adsorptive support--usually a metal phthalocyanine on an activated charcoal. The distillate is treated in contact with the supported metal chelate catalyst at oxidation conditions in the presence of an alkaline agent. The oxidizing agent is most often air admixed with the distillate to be treated, and the alkaline agent is most often an aqueous caustic solution charged continuously to the process or intermittently as required to maintain the catalyst in a caustic wetted state. (Gleim, U.S. Pat. No. 3,108,081)
The prior art has taught that in the preparation of a catalytic composite the support material is impregnated with the phthalocyanine catalyst from an aqueous solution of the catalyst, and that small amounts of an alkaline material such as sodium hydroxide can be used to increase the solubility of phthalocyanine catalyst in water. (Gleim, U.S. Pat. No. 3,108,081) The prior art has also taught that although water is the preferred solvent for the caustic which is injected into the hydrocarbon stream during the petroleum distillate treating process, other solvents such as alcohols can be employed to promote mercaptan solubility. (Gleim, U.S. Pat. No. 3,108,081) The prior art has disclosed certain catalytic composites comprising certain weakly basic materials impregnated on a solid adsorptive support. The weak bases disclosed are alkanolamine hydroxides, quaternary ammonium hydroxides, and carboxylic acids. (Frame, U.S. Pat. No. 4,159,964; Frame, U.S. Pat. No. 4,206,079; Carlson, U.S. Pat. No. 4,141,819) The art discloses that the weak bases can be impregnated on the adsorbent support from an aqueous or alcoholic solution.
What is not disclosed by the prior art is a catalytic composite comprising a metal chelate and an alkali metal hydroxide disposed on an adsorptive support wherein the composite is prepared from an alcohol admixture of support, metal chelate, and alkali metal hydroxide, wherein the admixture is dried at temperatures less than about 30.degree. C., and wherein the resulting catalytic composite comprises at least about 10 wt. % alkali metal hydroxide. The catalytic composite of this invention can be used very effectively in the treating process of this invention with or without the necessity of addition of an alkaline agent. The consequent savings in materials handling and storage expenses, and avoidance of use of hazardous alkaline chemicals in the treating process, have been long desired.